scholarly journals Placer gold occurrences along the major rivers of Nepal Himalaya and their possible primary sources

1996 ◽  
Vol 13 ◽  
Author(s):  
K. P. Kaphle ◽  
P. R. Joshi ◽  
H. R. Khan
Keyword(s):  
Gold Mineralization ◽  
Gold Deposits ◽  
Primary Sources ◽  
Gold Content ◽  
Lower Paleozoic ◽  
Nepal Himalaya ◽  
Placer Gold ◽  
Flood Plains ◽  
River Flood ◽  
Primary Gold

Recent exploration in Lungri Khola area, Rolpa district, midwestern Nepal helped to delineate a discontinuous 1.5 to 40 m thick and about 30 km long primary gold mineralization zone in the Precambrian greenschists and Lower Paleozoic micaceous marbles of the Lesser Himalaya. The gold content in these lodes vary from 0.01 to 6.7 ppm. In eastern Nepal occurrences of primary gold is recorded in quartz-biotiteschist, amphibolite and pegmatite bodies in Sunmai and Bering Khola of Ilam district. Fine flakes of gold also occur in the pyritiferous quartz beds/lenses in chlorite-sericite phyllite and quartzite of Bamangaon polymetallic prospect, Dadeldhura district, far western Nepal. In this prospect the gold content is from 0.2 to 0.8 ppm, and one sample showed up to 14 ppm. Primary gold occurrences are also detected in few irregular quartz-pyrite veins and iron-copper sulphide bearing quartzite lying close to the amphibolite bodies. Some pyrite bearing radioactive quartzite beds in Banku Quartzite of Purchauni Crystalline Complex exposed at Boregad, Bangabagar, Baggoth and Jamari Gad area in Darchula and Baitadi districts, far western Nepal also contain gold. The gold content in the radioactive quartzite varies from 0.2 to 1.2 ppm and in some pyritiferous radioactive quartzite floats it reaches up to 5.06 ppm. The primary gold appears to be of synsedimentary, hydrothermal and possibly volcanogenic in origin. Placer gold is derived from primary sources and deposited at favourable locations along the river flood plains. Further investigations in similar geological terrain may help to identify economically viable primary as well as placer gold deposits in the Nepal Himalaya.

scholarly journals Typomorphic Features of Placer Gold from the Billyakh Tectonic Melange Zone of the Anabar Shield and Its Potential Ore Sources (Northeastern Siberian Platform)

Minerals ◽  
2020 ◽  
Vol 10 (3) ◽  
pp. 281
Author(s):  
Boris Gerasimov ◽  
Vasily Beryozkin ◽  
Alexander Kravchenko
Keyword(s):  
Native Gold ◽  
Gold Mineralization ◽  
Coarse Fraction ◽  
Gold Deposits ◽  
Primary Sources ◽  
The Arctic ◽  
Geochemical Data ◽  
Placer Gold ◽  
Anabar Shield ◽  
Tectonic Mélange

Precambrian shields and outcropped Precambrian rock complexes in the Arctic may serve as the most important sources of various types of mineral raw materials, including gold. The gold potential of the Anabar shield in the territory of Siberia has, thus far, been poorly studied. A number of primary and placer gold occurrences have been discovered there, but criteria for the prediction of and search for gold mineralization remain unclear. The main purpose of this paper was to study the typomorphic features of placer gold in the central part of the Billyakh tectonic mélange zone in the Anabar shield and to compare them to mineralization from primary sources. To achieve this, we utilized common methods for mineralogical, petrographic, and mineragraphic analyses. Additionally, geochemical data were used. As a result of this investigation, important prospecting guides were identified, and essential criteria for the prediction of and search for gold deposits were elucidated. The characteristics of the studied placer gold were specific for gold derived from a proximal provenance. These characteristics included the poor roundness of the native gold grains, a cloddy–angular and dendritic form, an uneven surface, and a high content of coarse-fraction native gold (0.5–2 mm), which was as high as 24% of the volume of analyzed native gold. In addition, we conducted a study on the mineralogical features of the gold-sulfide mineralization that was disseminated throughout a small exposure area of paleo-Proterozoic para- and orthogneisses in the Anabar shield basement. A comparison of mineral inclusions in the coarse-fraction native gold and mineral assemblages in the ore deposits showed that one of the possible primary sources for placer gold might be small bodies of metasomatically altered orthogneisses associated with large granitoid plutons.

Prospects of primary gold potential in southern Siberian platform based on study results for placer gold morphological and geochemical features

2021 ◽  
pp. 97-114
Author(s):  
Ivan Chetvertakov ◽  
Alexey Ivanov ◽  
Ekaterina Mikheeva ◽  
Tatyana Chikisheva ◽  
Tamara Yakich
Keyword(s):  
Siberian Platform ◽  
Geological Structure ◽  
Gold Deposits ◽  
Primary Sources ◽  
Placer Gold ◽  
Genetic Types ◽  
Study Results ◽  
Geochemical Property ◽  
Geochemical Studies ◽  
Primary Gold

Data on geological structure and minerals of the southern Siberian platform are presented. Placer and primary gold occurrences widespread in this region are briefly characterized. Based on placer gold morphological and geochemical property studies using electron microscopy, its four types are revealed. Conclusions are made about potential primary sources of various placer gold types. Using retrospective data and based on the authors’ placer gold morphological and geochemical studies, Ust-Ilimskaya, Chernorechinskaya and Buraevskaya gold areas are characterized, their prospects for discovering primary gold deposits of various genetic types are determined.

scholarly journals Primary gold mineralization in the Pre-Cambrian and lower Paleozoic rocks, Lungri Khola region, Rolpa district

1991 ◽  
Vol 7 ◽  
Author(s):  
P. R. Joshi
Keyword(s):  
Gold Mineralization ◽  
Minor Amount ◽  
Gold Content ◽  
Lower Paleozoic ◽  
Initial Deposition ◽  
Paleozoic Rocks ◽  
Paleozoic Carbonates ◽  
Host Rocks ◽  
Chlorite Schist ◽  
Primary Gold

Primary gold mineralization occurring in the Lungri Khola region is observed in the Pre­ Cambrian green schist facies and Lower Paleozoic micaceous marble and limestone. The Pre-Cambrian green schist facies comprising mainly of sericite and chloritic quartzite, chlorite schist, quartz-chlorite schist, chlorite phyllite and schistose pebble beds include a discontinuous auriferous zone which persists laterally for about 30 km extension from the Gajul khola in the west to the upper reaches of Gam khola in the east. The auriferous host rocks are found confined close to the contact with the overlying Lower Paleozoic carbonates. Eight distinct auriferous hosts are encountered in the Pre-Cambrian green schists facies. Occurrence of auriferous host in the Lower Paleozoic limestone and marble is rather irregular and insignificant So far minor quartz-carbonate veins have indicated the presence of gold. Finely disseminated gold with minor amount of pyrite, chalcopyrite and rarely arsenopyrite occurs in the above hosts. Visible gold ranging from 0.08 to 2 mm dimension has been recovered. Gold content of upto 6.7 gm/ton has been recorded but in general they show 0.1 gm/ton gold which is significantly 30 to 60 times higher in magnitude than the background value. Depending upon the type of the hosts, three possible models, namely (1) volcanogenic (2) hydrothermal and (3) syn-sedimentary, could be suggested for the origin of the primary gold mineralization which has later undergone remobilisation after the initial deposition.

scholarly journals Method for Revealing Placer Gold Source

2020 ◽  
Vol 4 (4) ◽  
pp. 273-281
Author(s):  
O. V. Vladimirtseva
Keyword(s):  
Gold Mineralization ◽  
Spatial Association ◽  
Gold Deposits ◽  
High Order ◽  
Placer Gold ◽  
Location Determination ◽  
Python Programming ◽  
Logical Information ◽  
Geomorphological Features ◽  
Primary Gold

Material characteristics of placer gold and geological and geomorphological features of placercontaining watercourses allow revealing the type of source that formed the placer. The studied area (the middle reach of theAdychaRiver, Verkhoyansk District, Yakutia) is characterized by highly developed placer gold mineralization both in ancient terrace sediments and high-order watercourses. The significant placer gold mineralization in the high-order watercourses, at very limited number of known bedrock gold deposits suggests the presence of not yet discovered bedrock gold mineralization. Revealing the type of sources of placer gold in young high-order watercourses allows to create prognostic and prospecting models for both potential placer and primary (vein) ore occurrences. The purpose of the study is to compile a logical-information algorithm, which, based on the most significant material and geological-geomorphological factors, will enable revealing the type of placer gold source and the possibility of its location discovery and probability of gold transportation continuation from the source. The study result is presented by a program (the Python programming language) that characterizes the type of placer gold source based on gold grain rounding degree, the presence of gold intergrowths with other minerals and the presence of heavy fraction. Assessment of the possibility of placer gold source location determination is based on geological and geomorphological factors: watercourse order, the type of placer, and spatial association with terraces of ancient erosion levels. The study of well-known gold placers using the created program allowed revealing gold placers  with supposedly primary gold source and other ones with the source in the form of a natural intermediate gold concentrator. A map of exogenous gold mineralization with forecast elements was also created, presenting areas promising for revealing primary gold mineralization (areas of presence of high-order watercourses with gold mineralization source) and areas of high-order watercourses promising for discovering gold placers (identified by analogy (in geological and geomorphological position) with watercourses with the known source in the form of natural intermediate gold concentrator.

scholarly journals Criteria for Determining the Genesis of Placers and Their Different Sources Based on the Morphological Features of Placer Gold

Minerals ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 381
Author(s):  
Zinaida Nikiforova
Keyword(s):  
Native Gold ◽  
Morphological Characteristics ◽  
Gold Deposits ◽  
Primary Sources ◽  
Gold Content ◽  
Placer Gold ◽  
Gold Particles ◽  
Search Criterion ◽  
Different Sources ◽  
Gold Bearing

Based on the identified typomorphic features of placer gold, a set of determined morphogenetic criteria is proposed to identify the genesis of placer gold content and different sources in the platform areas, which allow more correctly selecting search methods and improving the efficiency of forecasting ore and placer gold deposits.Goldparticles larger than 0.25 mm with signs of wind-worn processing indicate the formation of autochthonous aeolian placers.Gold particles with signs of wind-worn processing with a size of 0.1–0.25 mm, forming an extensive halo of dispersion, indicate the formation of allochthonous placers in Quaternary deposits.Deflationary (autochthonous) placers of native gold can be found by the halo of its distribution of toroidal and sphericalhollow forms, which, of course, are the search morphogenetic criterion of aeolian placers.The presence of disc-shaped and lamellar gold particles with ridgelike edges in alluvial placers is typical for placers of heterogeneous origin, formed due to deflation of proluvialplacers.The discovery of pseudo-ore gold in alluvial placers indicates the arrival of gold from intermediate gold-bearing sources of different ages and not from primary sources, which is a morphogenetic criterion for determining different sources of the placer.In modern gold placers, the presence of gold of a pseudo-ore appearance can serve as a search criterion for the discovery of gold-bearing conglomerates with high gold content. The developed method for diagnosing the genotype of placer gold by its morphological characteristics (alluvial, aeolian, pseudo-ore) can be successfully used by industrial geological organizations to search and explore ore and placer gold deposits.

scholarly journals A NEW GOLD ORE REGION IN TANZANIA

2018 ◽  
pp. 55-59
Author(s):  
V. Mykhailov ◽  
А. Tots
Keyword(s):  
Gold Deposit ◽  
Shear Zone ◽  
Gold Mineralization ◽  
Lake Victoria ◽  
Gold Deposits ◽  
Mobile Belt ◽  
Gold Content ◽  
Gold Ore ◽  
Metallogenic Zone ◽  
The Republic

Tanzania is one of the leading gold mining countries in the world and the discovery of new gold resources on its territory is an actual task. Known gold deposits are concentrated mainly in the northwest of the country, in the metallogenic zone of Lake Victoria, where they are associated with the Archean greenstone belts, and to a lesser extent – in the southwest, in the ore regions of Lupa and Mpanda, confined to the Ubendian Paleoproterozoic mobile belt. With regard to the eastern regions of Tanzania, where the Proterozoic structures of the Uzagaran mobile belt are developed, until recently in this region any significant manifestations of gold mineralization were not known. As a result of our research in the northern part of the Morogoro province of the Republic of Tanzania, a new previously unknown gold deposit Mananila was discovered. It is represented by a large volume, up to 400–450 m long, up to 60–80 m thick, mineralized shear zone over intensely leached and schistosed migmatites, gneisses, amphibolites, penetrated by echelon systems of quartz veins and veinlet, steeply dipping bodies of quartz breccia up to 1.0–1.5 m thick. Gold contents range from 0.61 to 8.11 g/t, the average zone content is 2.5–3.0 g/t. Parallel to the main zone, similar structures are developed on the site, although they are of lower thickness. The forecast resources of the deposit are estimated at 20 tons of gold. 2.8 km to the east from the Mananila field, the recently discovered Mazizi gold deposit is located, and a number of small occurrences of gold are also known in the region. All these objects are located within a large shear zone of the northeastern strike, up to 4–5 km width, over 20 km in length. This serves as the basis for the identification of a new gold ore region in the northern part of the Morogoro province of the United Republic of Tanzania, within the Proterozoic mobile belt of Usagaran, the possible gold content of which has never been previously discussed in geological literature.

scholarly journals Giant Placers of the Victorian Gold Province

SEG Discovery ◽  
2004 ◽  
pp. 1-18
Author(s):  
Martin J. Hughes ◽  
G. Neil Phillips ◽  
Stephen P. Carey
Keyword(s):  
Late Cretaceous ◽  
Quartz Vein ◽  
Late Eocene ◽  
Gold Deposits ◽  
Gold Production ◽  
Placer Gold ◽  
High Rainfall ◽  
Hydrothermal Quartz ◽  
Alluvial Gold ◽  
Primary Gold

ABSTRACT The Victorian gold province has yielded 2500 tonnes (t) Au, nearly 2 percent of cumulative world gold production, mostly mined between 1851 and 1910. Fifty-five percent (1375 t) was placer gold from modern and paleostream systems, and from eluvial deposits, and the remainder came from primary quartz vein-related deposits. Most of the alluvial gold placers are in unconsolidated or weakly cemented quartz pebble conglomerate and gravel, dominated by hydrothermal quartz, although a few paleoplacers are within duricrusted conglomerate that required crushing. Large and abundant gold nuggets were common. Placer gold deposits formed in three intervals following uplift in the Late Cretaceous, Late Eocene, and Pliocene. An important factor in the preservation of the paleoplacers has been their burial by younger sediments and basalt flows, with consequent protection from erosion and dispersal. Factors in the formation of the giant gold placers of Victoria include the following: (1) the existence of a major primary gold province with several multimillion-ounce gold deposits; (2) uplift and reactivation of older faults; and (3) high rainfall and deep Paleogene weathering.

Tracing gold nuggets back to the source: a microchemical analysis of tertiary gold placers in Central Spain.

2021 ◽  
Author(s):  
Santos Barrios ◽  
Juan Gómez Barreiro ◽  
Rafael Pablo Lozano Fernández ◽  
Raúl Merinero Palomares ◽  
Mercedes Suárez Barrios ◽  
...  
Keyword(s):  
Primary Sources ◽  
Lower Paleozoic ◽  
Gold Particles ◽  
Fine Grained ◽  
In Situ Modification ◽  
Basement Rocks ◽  
El Alto ◽  
Alkaline Conditions ◽  
Fe Oxyhydroxides ◽  
Primary Gold

<p>Gold placers are abundant and intensively surveyed in western Iberia since antiquity. Three Cenozoic gold placers covering Neoproterozoic-Lower Paleozoic basement rocks have recently been revealed, which stand out for the number and size of the samples recovered: Salvatierra de Tormes (ST), Santibáñez el Alto (SA) and Casas de Don Pedro-Talarrubias (CSDP). To date, primary sources remain undiscovered. We have combined microchemical, inclusion analysis and morphology of gold nuggets to define the placer gold signature and its relationship with bedrock primary sources and infer mineralization styles. Coarse gold particles prevent secondary resetting of source signature and increase the chances to investigate mineral assemblages. Nuggets morphology analysis have reveled that ST and SA deposit are fluvial "trunk" placers, while CSDP represents an autochthon or colluvial placer type. Four different types of gold have been defined in nuggets: core gold (T1), rim gold (T2) fine grained gold in Fe-oxyhydroxides aggregates (T3) and "mustard" gold (Au+Sb-Pb-Fe-oxides) (T4).</p><p>Based on those categories we have explored primary and secondary signatures in the deposits. Lode signature is observed in the core of nuggets (T1) with a fineness between 800 and 1000. Alloy composition ranges from binary (Au:Ag) in SA to ternary (Au:Ag:Cu) in ST and CSDP. Sulphides and sulfarsenides dominates inclusions association in ST, while Sb- and Sb-Pb-Fe phases appear in ST and CSDP respectively. CSDP primary gold shows a distinct Hg content. The identification of mineral phases non-compatible with supergene conditions in gold and textural remnants of annealing microstructures, point to an hypogenic origin of T1 in all deposits and coul be compatible with a mesothermal system (<400ºC) in which, CSDP represents the higher T and SA the lower T end. A hybrid hydrothermal-magmatic system is proposed.</p><p>Secondary signature is complex and reveals several stages. Older evidence of in-situ modification of primary gold was found in CSDP gold-bearing quart fragments, with pervasive alteration under oxidizing and alkaline conditions. This process liberated gold from T1 and primary phases (e.g., aurostibite), leading to the formation of auroatimonades and "mustard" gold (T4), showing a complex textural pattern. Gold particles were subsequently modified during fluvial transport and deposition through the interaction with fluids, which activated Ag-leaching processes, resulting in the development of gold-rich rims (T2). Partial dissolution and re-precipitation of gold in reduction conditions formed very fineness gold particles embedded in Fe oxy-hydroxides (T3).</p>

scholarly journals ON THE GOLD MINERALIZATION IN WEATHERING CRUSTS OF THE RYBACHY SITE (WESTERN SIKHOTE-ALIN)

2021 ◽  
Vol 24 (1) ◽  
pp. 26-33
Author(s):  
E.V. Nigai
Keyword(s):  
Gold Mineralization ◽  
Raw Materials ◽  
Volcanic Belt ◽  
Gold Deposits ◽  
Gold Content ◽  
Mountain Areas ◽  
Alluvial Deposits ◽  
Weathering Crusts ◽  
Folded Structures ◽  
Eastern Institute

The author addresses an issue of gold presence in pre-Quaternary crusts of weathering that are widespread in sub-mountain areas of the doming-block geomorphological structures of the Amur Region, the Khabarovsk and Primorsky Territories along the periphery of large- and medium-sized Cenozoic basins and depressions. For a more detailed mining and geological study and assessment of the gold content of the weathering crusts, we recommended the Rybachy site as one of these objects (insufficiently studied), and the entire Mukhenskaya area as a promising one. These sites are located in the zone of articulation of the eastern side of the Middle Amur Depression with the folded structures of the West Sikhote-Alinsky volcanic belt. The author gives examples of large gold deposits, related to weathering crusts with their brief description (Olympiada, Kuranakh), as well as a brief description of alluvial deposits of weathering crust (sub-basalt cl.Paskhalny, an eluvial-alluvial placer of the Bolotisty Stream). The search work of the DVIMS (Far Eastern Institute of Mineral Raw Materials) in 2002 indicated the potential of weathering crusts within the Rybachy prospect for gold mineralization. This is supported by elevated gold in heavy mineral concentrates from the linear weathering crusts and residual blankets, as well as from non-commercial placers (from 0.01 to 4.0 g/t and higher); the occurrence of fracture zones, brecciation, secondary silicification close by fractures, and abundant Late Cretaceous silicic and intermediate dikes. Zones of hydrothermally altered rocks (silicification, chloritization, sericitization, argillization) are widespread here.

scholarly journals Types of Tellurium Mineralization of Gold Deposits of the Aldan Shield (Southern Yakutia, Russia)

Minerals ◽  
2021 ◽  
Vol 11 (7) ◽  
pp. 698
Author(s):  
Larisa A. Kondratieva ◽  
Galina S. Anisimova ◽  
Veronika N. Kardashevskaia
Keyword(s):  
Large Scale ◽  
Native Gold ◽  
Gold Mineralization ◽  
Aldan Shield ◽  
Original Data ◽  
Gold Deposits ◽  
Ore Deposits ◽  
Gold Content ◽  
Southern Yakutia ◽  
Igneous Activity

The published and original data on the tellurium mineralization of gold ore deposits of the Aldan Shield are systematized and generalized. The gold content is related to hydrothermal-metasomatic processes caused by Mesozoic igneous activity of the region. The formation of tellurides occurred at the very late stages of the generation of gold mineralization of all existing types of metasomatic formations. 29 tellurium minerals, including 16 tellurides, 5 sulfotellurides and 8 tellurates have been identified. Tellurium minerals of two systems predominate: Au-Bi-Te and Au-Ag-Te. Gold is not only in an invisible state in sulfides and in the form of native gold of different fineness, but also is part of a variety of compounds: montbrayite, calaverite, sylvanite, krennerite and petzite. In the gold deposits of the Aldan Shield, three mineral types are distinguished: Au-Ag-Te, Au-Bi-Te, and also a mixed one, which combines the mineralization of both systems. The decrease in the fineness of native gold is consistent with the sequence and temperatures of the formation of Te minerals and associated mineral paragenesis from the epithermal–mesothermal Au-Bi-Te to epithermal Au-Ag-Te. The conducted studies allowed us to determine a wide variety of mineral species and significantly expand the area of distribution of Au-Te mineralization that indicates its large-scale regional occurrence in the Aldan Shield.

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